This situation is like a very young child, who originally started out nice, became corrupt and mean by their parents' abusive behavior. Negative acts such as yelling, torturing, insulting, and abuse ruin the child's psychological thinking and he, too, becomes corrupt just like his/her parents. Over the course of a couple of years, if this child had friends, they would very well notice his change of behavior and personality.
I'm not saying you have abusive parents; this is just an example situation. The point I was trying to address was, yes, it can very well be easily noticed. Specially if you've had close friends for a very long time. Maybe you two became friends when you were happy, and over the course of several years, one participant is emo and the second one could notice it very well.
